Smart card technology for such applications as credit cards, identity cards, and secure access to computer systems and transportation is becoming more pervasive. Generally, a smart card contains a small, externally powered integrated circuit, such as a microprocessor mounted on a pocket size card. The integrated circuit can be programmed to interface to a smart card reader to authenticate financial transactions, provide secure access to computer systems, and verify identity, for example. Because the integrated circuit within the smart card is externally powered, a smart card typically has a number of electrical contacts on a face of the card, which can be interfaced to corresponding contacts of data and power interface within a smart card reader.
A typical smart card interface includes eight metal pads. Among these pads are a power pad and a ground pad, which is typically shared with the power system within the card reader. If someone were to insert a defective smartcard with shorted contacts or piece of sheet metal within the card reader, however, a short circuit between the power and ground pads of the smart card reader could result. Such a short circuit could disable the smart card interface and possibly shut down the system coupled to the smart card interface. Such a system shut-down is problematic, particularly in systems that perform financial transactions such as cash or banking machines.
In the past, the problem of short circuit protection within smart card readers has been addressed by using one-off fuses, self-reset fuses or isolated power supplies. One-off fuses are problematic in that the mechanism of the fuse takes a long time to act, thereby triggering a system reset after the onset of a short circuit at the smart card power supply interface. Furthermore, one-off fuses creates difficulties with system maintenance in that a triggered one-off fuse typically requires replacement or manual reset by a technician, which results in down-time and loss of profit from revenue generating machines.
A smart-card system using a self-reset fuse can restart once the short circuit condition is removed. Self-reset fuses, however, may take too long to trigger, may not provide adequate protection to the entire smart card system.
Another way to deal with the problem of a short circuit between power contacts of a smart card reader is to isolate the smart card power supply from the main power supply, for example, by using a separate and independent power supply. A short circuit on the smart card interface will, therefore, not affect the power supply for the whole smart card system. The extra power supply is more expensive to manufacture, and still leaves the smart card power supply vulnerable to damage caused by short circuits.
FIG. 1 illustrates smart card reader system 100 according to the prior art. System 100 has power supply 102, connector interface 106, and smart card reader electronics 104. Power supply 102 supplies power to the entire smart card reader system, and smart card reader electronics 104 contains, for example, a microprocessor or microcontroller, memory and interface electronics to perform the functions of the smart card reader. Connector interface 106 is physically configured to accept a smart card and has a plurality of connector terminals 108, 110, 112, 114, 116, 118, 120 and 122 that make contact with a smart card (not shown). Power to the smart card is supplied by power pin 108 and ground pin 110. Global ground 101 is supplied to power supply 102, smart card reader electronics 104 and connector interface 106.
If power pin 108 is connected to ground pin 110 forming short circuit 130, a high current ISS will result. Such a short circuit can be formed, for example, by a inserting a defective or damaged smart card into connector interface 106, or by inserting a slug or a piece of sheet metal into connector interface 106. If the sum of ISS and the current drawn by the rest of the system is greater than the rated current of power supply 102, damage to power supply 102 and/or system failure may result.
In the field of power supplies, what are needed are cost effective systems and methods that quickly detect and disable a short circuit condition in one portion of a system without affecting the performance of the remaining portions of the system.